1. Field of the Invention
The present invention relates to a solenoid driving device for controlling an electric current to be fed to a solenoid.
2. Related Art
In the prior art, a hydraulically driven vehicle such as a construction machine is provided therein with a solenoid driving device including: a solenoid for driving an electromagnetic valve (or an electromagnetic proportion control valve); and a controller for controlling an electric current to the solenoid.
The device of this kind is known, as shown in FIG. 25 or FIG. 26.
In FIG. 25, the left-hand side of a dotted line shows the (inside) of a controller side, and the right-hand side shows a solenoid (or an electromagnetic valve) side.
In this device shown in FIG. 25, a solenoid 1 is connected at its two end portions 1A and 1B, respectively, through signal lines (or wire harnesses) 2A and 2B with terminal portions 3A and 3B of a connector 3, as disposed on the controller side. Generally, the electromagnetic valve or solenoid 1 is arranged at a position spaced from the controller, and these components are connected by the signal lines 2A and 2B of about 1 to 2 m.
On the controller side, on the other hand, the anode (+) side of a DC load power source VB is connected with the terminal portion 3A of the connector 3 through a switch SW for pulse modulations, and a current detector 4 is connected between the terminal portion 3B of the connector 3 and the GND (or ground). In short, the current detector 4 is disposed on the low side (or the GND side) with respect to the solenoid 1.
Between the terminal portion 3A of the connector 3 and the GND, there is connected a free-wheel diode D which is connected at its cathode with the terminal portion 3A and at its anode with the GND.
The switch SW is constructed to include a switching element such as a transistor or a field effect transistor and is turned ON/OFF (or switched) according to a pulse-width modulation signal (or a PWM signal).
When this switch SW is ON, the electric current from the anode side of the load power source VB flows to the solenoid 1 through the switch SW, the terminal portion 3A of the connector 3 and the signal line 2A and further to the GND through the signal line 2B, the terminal portion 3B of the connector 3 and the current detector 4. At this time, the current detector 4 detects the electric current having from the solenoid 1 and outputs the detected result. This detected result is used as the signal for controlling the electric current to flow to the solenoid 1, that is, the signal for determining the duty ratio of the pulse-width modulation signal to turn ON/OFF the switch SW.
As a result, the electromagnetic valve (or the electromagnetic proportion control valve) in response to the action of the solenoid 1.
On the other hand, the device shown in FIG. 26 is modified in the arrangement of the current detector 4 and the switch SW from the construction of the device shown in FIG. 25. Here in FIG. 26, the portions for performing the same functions as those of the components shown in FIG. 25 are designated by the common reference numerals.
Now in FIG. 26, the current detector 4 is arranged on the high side (or on the power source side) with respect to the solenoid 1, and the switch SW is connected with the GND.
Specifically, the current detector 4 is connected between the load power source VB and the terminal portion 3A of the connector 3, and the switch SW is connected between the terminal portion 3B of the connector 3 and the GND. Between the input side of the current detector 4 and the terminal portion 3B of the connector 3, on the other hand, there is connected the free-wheel diode D which is connected at its cathode with that input side and at its anode with that terminal portion 3B.
In this case, when the switch SW is ON, the electric current from the anode side of the load power source VB flows to the solenoid 1 through the current detector 4, the terminal portion 3A of the connector 3 and the signal line 2A and further to the GND through the signal line 2B, the terminal portion 3B of the connector 3 and the switch SW. At this time, the current detector 4 detects the electric current to flow through the solenoid 1 and outputs the detected result. This detected result is used like before as the signal for determining the duty ratio of the pulse-width modulation signal to turn ON/OFF the switch SW.
Here in the devices shown in FIGS. 25 and 26, the controller controls only one solenoid. As a matter of fact, however, the controller controls a plurality of solenoids, as shown in FIGS. 27 and 28. In these solenoid driving devices shown in FIGS. 27 and 28, the controller is given a construction similar to that of the controller (or the controller inner side) of the device shown in FIG. 25 or 26 for one solenoid. Here in FIGS. 27 and 28, there are omitted the reference numerals for designating the signal lines and the end portions of the solenoid.